X-ray method



May 5, 1959 G. DESTRLAU Ax-RAY METHOD Filed May 13, 1957 2 Sheets-Sheet l 5.6.5UPPLY May 5,y 1959 Filed May 13, 1957 G. DESTRIAU X-RAY METHOD 2 Sheets-Sheet 2 INVENTOR.

BY www* United States Patent X-RAY METHOD Georges Destriau, Cauderan, France, assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application March 13, 1957, Serial No. 645,742 Y' 9 claims. (ci. 25o-711) 'This invention relates to X-ray-electroluminescent devices and, mcre particularly, to a method for operating a uoroscopic system.

In the operation of iluoroscopic devices, theimages are produced by contrast differences between individual portions of such images. It is desirable in some cases to increase the contrast obtainable in the images. Also, it may be desirable for some limited applications to decrease the contrast in the images. In addition, it is desirable to enhance the brightness of the images produced on a uoroscopic screen without substantially increasing the quantity of X-ray irradiation used to generate the X-ray signal.

' It is the general object of this invention to provide a method for varying the contrast in the luminous response to van X-ray signal of an X-ray-responsive phosphor screen.

It is a further object to provide a method for simultaneously increasing the brightness and the contrast of the luminescent response to an X-ray signal of an X-rayresponsive phosphor screen.

It is an ladditional object to provide a method for enhancing the brightness and, if desired, the contrast of the luminescent response to an X-ray signal of an X-rayresponsive phosphor screen, without appreciably increasing the quantity of the X-ray signal irradiation used to excite the screen.

The aforesaid objects of the invention, and other objects which will become apparent as the description proceeds, are achieved by providing a process for operating an X-ray apparatus incorporating an X-ray-responsive phosphor screen characterized by displaying an enhanced luminous outputwhen excited by X-rays and simultaneously placed within the iniluence of an alternating electric iield. In the operation of this apparatus, the phosphor screen is presensitized by applying thereto the X-ray signal for which the contrast is to be varied and simultaneously applying across the screen an alternating electric field. The initial screen-presensitizing X-ray signal irradiation is then stopped and the screen is removed from the influence of the alternating electric eld. The screen is thereafter irradiated with the same X-ray signal pattern as previously, but preferably with an increased X-ray intensity. This causes the screen to produce a luminous image corresponding to the applied X-ray signals, but with a varied and preferably enhanced contrast between the brightest and the darkest portions of the luminous image.

For a better understanding o f the invention, reference should be had to the accompanying drawings, wherein:

Fig. 1 is a sectional elevation of the preferred X-rayelectroluminescent fluoroscopic screen;

Fig. 2 is a schematic diagram of the X-ray unit andv operating circuit therefor, illustrating the phosphor screen presensitizing operation; v

Fig. 3 is a schematic diagram similar to Fig. 2 illustrating the second phase of the equipment operation,-

' temperature of from 800 In Fig. l is illustrated the preferred embodiment of vable bus bars 20 and to the electroluminescent field-voltage supply described ICC wherein the image is produced on the tluoroscopic screen with improved contrast;

Fig. 4 is a graph of the ratio of enhanced output vs. X-ray irradiation of a presensitized fluoroscopic screen;

Fig. 5 is a graph of brightness in arbitrary units vs. time illustrating the operation of the unit so that the contrast between the brightest and darkest portions of the iluoroscopic image is varied.

Although the principles of the invention are broadly applicable to any system wherein an X-ray-responsive phosphor of the type specified herein is to be irradiated by X-rays, the invention has particular reference to tluoroscopic screens which are fabricated similar to an electroluminescent cell and hence it has been so illustrated and will be so described.

In copending application of G. Destriau, the inventor herein, S.N. 433,185, filed May 28, 1954, titled X-ray Electroluminescent Screen and assigned to the present assignee, is disclosed an X-ray-elec'troluminescent device wherein the output of the X-ray-responsive phosphor is enhanced by the simultaneous application of an electric eld across the phosphor. This enhanced output enables a smaller dosage of X-rays to be used in order to achieve a usable brightness of the fluoroscopic screen or, alternatively, makes possible a brighter picture without increasing the dosage of X-rays. The phosphor materials which may be used in this copending application are those which will display an enhanced luminous output when excited by X-rays and simultaneously placed within the inuence of an alternating electric field. This is contrary to the action of most phosphors which will display a quenching effect under similar conditions.

The phosphors which may be used in the instant system are those which may be used in the so-called X-ray enhancement as disclosed in the heretofore-mentioned copending Destriau application, namely, those phosphors which display an enhanced output when irradiated with X-rays and simultaneously placed within the inuence of an alternating electric eld. Specific phosphors which will be suitable for the instant purpose are mixtures of zinc sulde and cadmium sulde wherein the molar ratio of zinc to cadmium is from nine mole parts zinc, one mole part cadmium to three mole parts zinc, seven mole parts cadmium and activated by from 0.01)(10-2 to 6.0)(10-2 mole of manganese per mole of luminescent material. vIn addition, the phosphor material may be activated by a mixture of manganese and silver, with the silver being present in amounts of from traces (0.001 X 10*2 mole silver per mole manganese) up to about 1.0 l02 mole silver per mole manganese. Also, zinc sulfide phosphors which are activated with manganese or mixtures of manganese and silver in the heretofore-disclosed amounts are also suitable. As a specific example, the phosphor material may comprise 1CdS3.5ZnS, activated by 1x10-4 mole manganese per mole of luminescent material, such a phosphor having been fired during preparation at a C. t0 1150 C.

the electroluminescent-uoroscopic screen 10 which comprises a substantially planar layer of luminescent material 12 adjacent a substantially planar layer of di- 'electric material 14 with the luminescent and dielectric materials being sandwiched beween two thin, conducting layers or electrodes 16 and 18. Each of the electrode layers 16 and 18 may be connected through suitsuitable electrical connection 22 hereinafter. A foundation-viewing plate 24 is placed over one of the conducting layers, for example electrode layer 18 and an insulating layer 26 may be placed over the other conducting electrode layer 16 in order to miniassignee mize shock hazard. A protecting and handling shield 28 may be provided around 'the entire periphery of the screen in order to facilitate storage, handling, etc.

The luminescent material layer 12 is preferably positioned `next to the 'foundation-viewing plate 24, although for some applications it .may be preferable to place the dielectric layer 14 next 'to the viewing plate 24. 'T he thickness of the luminescent material layer `L12 is not particularly critical, but as a specific example it may `have :a thickness of 0.2 mm. The dielectric layer 14 'may comprise any 'suitable dielectric which has a high dielectric constant, is transparent :to either visible light or to '.X-rays dependingupon its position within thescreen, and :will not rapidly deteriorate under the action of X- rays. Such materials are wellknown and as an example, the dielectric material layer `14 may .comprise a mica sheet about 10.05 mm. thick, although this thickness is in `no "way critical and may be increased or decreased as indicated by the application.

Alternative constructions are also possible in the screen 10 and a suitable light-transmissive dielectric material such as polyvinyl-chloride acetate may be admixed with the phosphor and the separate layer of dielectric material .dispensed with, if desired, or the dielectric material may be dispensed with entirely in some special applications and only the phosphor layer 12 placed between Vthe electrodes 16 and 18. It should be pointed out that the purpose of the dielectric material is to prevent electrical breakdown through the phosphor and between the electrodes '16 and 18 and the electric fields as may be used herein need not be particularly intense. The usable electric fields, however, may vary over a wide range as in the heretofore-mentioned copending Destriau application and as a specific example, the electric iield which is applied across the screen during screen presensitization may have an intensity of 20 kv. per cm.

The conducting electrodes 16 and 18 may be fabricated of any conducting materials which may be coated as a thin sheet and are transmissive to visible light in the case of the lower layer 18 and transmissive to X-rays in the case of the upper layer 16. Of course these electrodes should not deteriorate appreciably under the action of X-rays. As an example, the electrode 18 ,may be fabricated of a thin layer of tin oxide on a glass base, such as sold under the trademark NESA by Pittsburgh Plate Glass Co., Pittsburgh, Pa. Other suitable thin, conducting coatings such as oxides of zinc, cadmium, aluminum or bismuth, for example, may also be used. The electrode 16 may be fabricated of tin oxide, for example, or it may be a thin coating of aluminum which may be applied by the well-known vacuum-metalizing techniques. The thin, protective layer 26, which is intended to insure against shock hazard and to facilitate handling, may be fabricated of any X-ray-transrnissive material which has relatively good electrical insulation properties and plastics such as polytetrauoroethylene are suitable. The protective layer 26 may be dispensed with, if desired, and the shock hazard eliminated by grounding the electrode 16. The foundation glass-viewing plate is normally fabricated of any glass which contains heavy atoms which will absorb the X-rays and thus protect the viewer or the photographic plate, as the case may be. As an example, any of the well-known lead or cerium glass may be used. The protecting and handling shield 2S may be fabricated of a plastic similar to the layer 26 and this shield may be dispensed with, if des-ired.

In Fig. 2 is illustrated, in block diagram, one embodiment of a suitable X-ray apparatus which in this showing is set for initial exposure of the object being X- rayed in order to presensitize the uoroscopic screen 10. This apparatus 30 comprises an X-ray rectifier and transformer unit 32, X-ray and lm shutter timer 34, X-ray tube 36, feld-voltage-control unit 38, field-timer unit 40, the X-ray uoroscopic screen 10, exposure switch 42, field-electric switch 44, camera film 46, camera shutter tripping unit 43 and camera shutter 50. All of the components of this apparatus are well known with the exception of the X-ray-tluoroscopic screen 10 which has been described in detail hereinbefore, and which screen may be identical, if desired, with the corresponding screen described inthe'heretofore-mentioned copending Destriau application. The use of automatic timers may be eliminated, if desired, and the entire timing `sequence may be carried outby hand.

ln Fig. 3 is shown in block diagram the sameX-ray apparatus Aas shown in Fig. 2, but with the electric lield switch -44 in an openposition. With the X-ray uoroscopic screen presensitized, the apparatus is thus set to again irradiate theobject being X-raye'd in order to produce on the iiuoroscopic screen a corresponding image with excellent contrast. The details of the operation of this apparatus will be considered as Vthe description proceeds. '1:"orjpurposes of explanation, the object'fSZ'being X-rayed has been shown as having one portion with twice the X-ray permeability as the remaining portion.

`In explanation of the term fscreen presensitization, it has been found that when afluoroscopic screen of the type described herein is'irradiated with an X-'ray signal and simultaneously placed within the influence of an alternating electric eld, a portion of the luminous `respouse developed by the screen-applied X-ray signal will be imparted'to the screen. This isterme'd screenpresensitization. This `screen-imparted signal may be released from the so-called vpresensitized screen lby a second 'X-ray irradiation. In copending application 'of G. Destriau, the inventor herein,rtitled X-Ray System, S.N. 645,694, led concurrentlyherewith and assigned to the present assignee, is described an X-ray apparatus similar to the instant apparatus and a method for operating same wherein the screen is Vpresensitized as in the instant method. After presensitization, however, the object being X-rayed is removed from between the X-ray tube and the screen Vand the memorized signa may be released from the presensitized screen. The instant method diers, however, in that the object is left between the tube 36 and the screen 10 after screen presensitization and on second X-ray irradiation of the presensitized screen with the X-ray signal, the object image can be reproduced thereon with varied contrast and, if desired, with increased brightness.

In Fig. 4 is shown a graph of enhancing ratio vs. second X-ray irradiation, expressed as milliamperes of current drawn by the X-ray tube 36. In arriving at these curves, thescreen 10 waspresensitized and the screen brightness was measured with no object between the screen and the X-ray tube 36 when it drew indicated currents. Of course, inclusive of an object on the X-ray table requires a greater quantity or intensity of X-ray irradiation, to deliver to the screen 10 an equivalent quantity of X-rays (in the case of the presensitizing step) or an equivalent intensity of X-rays (in the case of the second irradiation).

Each of the curves in Fig. 4 indicates the relative brightness ratio for a different presensitizing quantity (Q) of X-rays, as follows: Curve A, Q=640 microampere minutes (aa. min); Curve B, Q=320 fia. min.; Curve C, Q=160 ga. min.; Curve D, Q=80 garmin.; Curve E, Q=40 lia. min.; Curve F, Q=2O pa. min.; Curve G, Q=l0 aa. min.; Curve H, Q=5 ua. min. The X-ray tube 36 as used herein had a hard glass window and was operated at a voltageof kv. with a self-rectified circuit. The target material was tungsten and the distance from the centerline of the tube 36 to thescreen 10 was 2() cm. Under these conditions of operation, the tube`current and time were measured'to the indicated values of Q. It should be understood that these conditions of operation may be varied considerably, depending on the application. The brightness ratio is also dependent upon the intensity of the second X-ray-signal irradiation of the screenfandthisisplotted las the -abscissa `in -these curves.

seafront In the relative brightness ratio, Bm is the maximum brightness in arbitrary units for a presensitized screen and Bo is the maximum brightness in arbitrary units for an unsensitized screen irradiated with equal-intensity X-rays.

In Fig. 5 is illustrated the operation of the equipment in order to improve the contrast of the resulting image. For purposes of simplification, the object being X-rayed is represented as comprising two portions, one of which has twice the permeability to X-rays as the other portion. The object 52 is placed on the X-ray table and, as an example, is irradiated with X-rays of such intensity that the portions of the screen adjacent the more X-raytransmissive portion of the object will receive a quantity of X-ray irradiation equivalent to a total Q of 160 pa. min. Simultaneously with the X-ray irradiation, the electric field as indicated hereinbefore is applied across the screen since the switch 44 is in the closed position, see Fig. 2. Preferably, the X-ray irradiation is removed just before the field is removed. The brightness of the screen with the simultaneously-applied X-rays and field will follow the general line O-T-U for the screen portions adjacent the more X-ray transmissive portions of the object. The screen brightness will follow the line O-T-U for the screen portions adjacent the more X-ray opaque portion of the object being X-rayed, which screen portions will receive a quantity of X-ray irradiation equivalent to a Q of 80 na. min. This procedure presensitizes the screen 10. It should be noted that the screen prcsensitization is not effected by the field alone, nor will the field alone, as specified, develop any appreciable pure electroluminescence in the screen 10.

In the illustrated examples, a generally-linear response of X-ray intensity to screen brightness is realized and the brightest portions of the screen will be twice as bright as the darkest portions of the screen, as indicated by the relative brightness of the ordinates at points U and U. It should be noted that Without the simultaneous application of the electric field across the screen, the screen brightnesses may be approximately one-fifth those which are represented.

In the foregoing example of the operation of the unit, the field is shown as being discontinued at point V, and this may be ten seconds, for example, after the presensitizng X-ray irradiation is stopped. Immediately thereafter, while the object is still remaining stationary on the viewing table, the object 52 may be again irradiated with much more intense X-rays. Of course, the initial X-ray irradiation could be removed simultaneously with the field, or shortly thereafter. The latter procedure, however, would sacrifice some screen presensitization.

Referring now to Fig. 4, in the example given the screen has been presensitized. with a quantity of X-rays equivalent to a quantity of Q=l60 ha. min. and Q=80 na. rnin., curves C and D. If the second X-ray irradiation (j) is of such intensity that the screen portion adjacent the more X-ray-transmissive portion of the object will receive an X-ray intensity equivalent to that produced when the tube i is drawing 1.4 milliamperes with no object in place, the brightness of the screen portions presensitized to a Q of 160 lua. min. will have a brightness-enhancing ratio of 2.66 to 1. Under this X-ray irradiation the brightness of the screen adjacent the more X-ray opaque portion of the body will receive the equivalent of j=0.7 milliamperes and will display a brightness-enhancing ratio of 1.9 to l.

Referring now to Fig. with a second X-ray irradiation of j=l.4 milliamperes, the curve of screen brightness vs. time would follow the general line O-Y. However,

since the screen has been presensitized, there will be generated thereon a transient image corresponding to the screen-presensitized image and to the object image corresponding to the second-applied X-ray signal. This tran-v sient image will follow the general line O-X-Y and at point Y the transient image will be expended and theA screen will luminesce with an intensity corresponding to" since the individual brightness ratios are 2.66:l and 1.9:1`

respectively for the more intense and weaker screen-signal irradiation, this will increase the contrast between the brighter and darker portions of the image generated on the screen. Thus in example given, the contrast in the image. produced on the screen will be improved from the ratio of 2:1, which would be realized with no screen presensitization, to the ratio of 2.8:1 which is actually realized.

It is also possible to decrease the contrast in the screen, although normally the contrast is desirably enhanced. As an example, decreasing contrast may be achieved by limiting the presensitizing X-ray irradiation of the screen so that the brighter portions are presensitized to a of 20 tta. min., and the darker portions are presensitized to the Q of 10 fra. min. With"presensitized screen X-ray-signal irradiation having intensities of j=l.4 and j=0.7 milliamperes, respectively, for the brighter and the darker portions of the image produced on the screen, the enhancing ratios will be 1.06:1 for the brighter portions and 1.14:1 for the darker'portions, which will decrease the contrast realized in the image.

It is also possible to maintain the contrast substantially uniform in the transient object image generated on the screen and this may be achieved by irradiating the object with X-rays in such quantity that the portion of the screen adjacent the more transmissive portion of thev object 52 is irradiated with an X-ray intensity equivalent to a Q of 20 ltta. min. (see Curve F, Fig. 4). This will cause the portions of the screen adjacent the more X-ray opaque portion of the object 50 to be irradiated with an X-ray intensity equivalent to a Q of 10 tra. min. (see Curve G, Fig. 4). Upon irradiation with a second-applied X-ray signal having an intensity of "j==l for the more transmissive portion of the object 52 and an intensity of j=0.5 for the more opaque portion of the object 52, the contrast in the transient image will remain substantially unchanged. The advantages to be realized from such a procedure are increased screen brightness without appreciable increase in the total quantity of X-rays to which the object 52 is exposed, as explained more fully hereinafter.

In the specific examples, as given, the field has been removed after removal of the first X-ray signal irradiation, but it should be understood that the field and the X-ray signal irradiation may be removed simultaneously with out impairing the operation and the second X-ray signal may be applied immediately thereafter. This of course could be accomplished by increasing the X-ray intensity and simultaneously removing the field.

The transient image, which achieves a maximtun of contrast at points X and X in Fig. 5, is'preferably relater. Referring to Fig. 3 when the switch 44 is raised to an elevated position to open the field timer unit 40,`

it renders operative the camera-shutter tripping unit 48. When the exposure switch 42 is closed, the timer unit 34 is actuated and at a predetermined time thereafter and the shutter-tripping unit 48 actuates the film shutter 50 to record the brightestportions of the transient image. Immediately thereafter the second X-ray irradiation may be stopped. This may be effected by opening exposure switch 42 or by setting the timer unit 34. As an example, the camera may record the image five seconds after the second X-ray signal irradiation of the screen 10 is started.

With the foregoing method of operation, it is possible to achieve an improvement in image contrast and a relatively bright X-ray image as compared to the image brightness `which would vbe obtained for an equivalent quantity of X-rays applied to the subject; In explanation, the screen presensitization can be effected with a relatively small quantity of X-rays. Thereafter, the X- ray intensitymay be greatly increased in order to obtain maximum luminosity and contrast in the image. This stronger-intensity X-ray signal, however, need only be of relatively short duration as the peak in luminosity is reached in a matter of seconds and once this peak is recorded photographically, the second and more intense X-ray irradiationrnay be stopped. It should be pointed out that the brightness of the image produced on the screen during the second X-rayvirradiation is not as great as would be obtained with the simultaneous application of an electric field across the screen while the screen was irradiated with equivalent intensity X-rays. The build-up in luminosity of the lenhanced brightness, however, is relatively slow and accordingly, the quantity of X-rays required to produce such ultimate enhanced luminosity is correspondingly great. In the instant system, the buildup in luminosity of the screen, upon application of the second and more intense X-ray signal, is quite rapid and immediately after the peak in luminosity has been reached, the second X-ray irradiation may be stopped. Thus the total quantity of X-rays to which the object is exposed need only be relatively small in order to obtain a bright image.

It should be noted that the foregoing method may be utilized in X-raying both animate and inanimate objects. If a living object is to be X-rayed and difficulty is anticipated in keeping the object stationary, the presensitization period may be shortened by increasing the X-ray intensity and decreasing the exposure time to achieve the desired value of Q (X-ray intensity times time). lmmediately thereafter the field may be removed and the X-ray irradiation simultaneously increased to the desired value in order to achieve the peak in luminosity, such as shown by point X in Fig. 5. Thereafter, the second X-ray irradiation is stopped.

As disclosed in the heretofore-mentionedand concurrently-fled Destriau copending application, the time interval between presensitization and the application of the second applied X-ray signal may be extended considerably, if desired, and even after 17 hours the presensitized screen still retains a considerable portion of the stored or memorized image. Also, irradiation of the presensitized screen with visiblel light or ultraviolet will impair the presensitization.

It will be recognized that the objects of the invention have been achieved by providing a method for varying the contrast in the luminous response to an X-ray signal of an X-ray responsive phosphor screen. In addition, the brightness of the screen may be enhanced simultaneously with the contrast, without appreciably increasing the quantity of X-ray signal irradiation which is used to excite the screen.

There is led concurrently herewith an application by G. Destriau, the inventor herein, S.N. 645,695, titled Method for Operating X- Ray Device, and assigned to the present assignee, a third method for operating `the X-ray system disclosed herein, wherein the screen is first presensitized without the object between the tube 36 and the screen 10. The object is then placed between the tube 36 and the screen 1d and a relatively intense X-ray irradiation is used to generate an X-ray signal.

While in accordance with the patent statutes, one bestknown embodiment of the invention has been illustrated and described in detail, itis to beparticularly understood that the invention is not limited thereto or thereby.

I claim:

l. The process of varying ,the contrast in the luminous response to an X-ray signal o fanX-ray-responsive phosphor ,Screen characterized 'by displaying@ @hanged luminous output `when irradiated by X-,rays and simultaneously placed within the` influence of an alternating electric field, said process comprising passing selected intensity X-.rays through a stationary object having varying permeability to X-rays to generate a first X-ray signal, applying to said screen said first X-ray signal and simultaneously applying across said screen an alternating electric field to eiect a phosphor-screen presensitization varying in degree according to the quantity of X-rays applied thereto, removing from said presensitized screen said applied X-ray signal and said applied electric field, repassing selected intensity X-rays through said object to generate a second X-ray signal, and applying said second X-ray signal to said screen to produce thereon a transient luminous object image varying in luminosity with the varying X-ray intensity of said second X-ray signal and with the degree of screen presensitization previously effected, whereby the contrast between individual portions of the transient object image formed on said screen is varied.

2. The process of increasing the contrast in the luminous response to an X-ray signal of an X-ray-responsive phosphor screen characterized by displaying an enhanced luminous output when irradiated by X-rays and simultaneously placed within the influence of an alternating electric field, said process comprising passing selected intensity X-rays through a stationary object having varying permeability `to X-,rays to generate a first X-ray signal, applying to said screen said lirst X-ray signal and simultaneously applying across said screen an alternating electric field to effect a phosphor-screen presensitization varying in degree according to the quantity of X-rays applied thereto, removing from said presensitized screen said applied X-ray signal and said applied electric field, repassing selected intensity X-rays through said object to generate a second X-ray signal, and applying said second X-ray signal to said screen to produce thereon a transient luminous object image varying in luminosity with the varying X-ray intensity of said second X-ray signal and with the degree of screen presensitization previously effected, whereby the contrast between individual portions of the transient object image formed on said screen is increased.

3. The process of increasing the contrast in the luminous response to an X-ray signal of an X-ray-responsive phosphor screen characterized by displaying an enhanced luminous output when irradiated by X-rays and simultaneously placed within the influence of an alternating electric field, said process comprising passing selected intensity X-rays through a stationary object having varying perrmeability to X-rays to generate a first X-ray signal, applying to said screen said first X-ray signal and simultaneous/ly applying across said screen an alternating electric field to eiiect a phosphor-screen presensitization varying in degree according to the quantity of X-rays applied thereto,`rem`oving from said presensitized screen said applied X-ray signal and said applied electric field and immediately repassing selected intensity X-rays through said object to generate a second X-ray signal, and applying said second X-ray signal to said screen to produce thereon a transient luminous object image varying in luminosity With the varying X-ray intensity of said second X-ray signal and with'the degree of screen presensitization previously effected, whereby the contrast between individual portions of the transientobject image formed on said screen is increased.

4. The process of increasing the contrast in the luminous response to an X-ray signal of an X-ray-responsive phosphor screen characterized by displaying an enhanced luminous output when irradiated by X-rays and simultaneously placed within the influence of an alternating electric field, said process Ycomprising passing selected intensity X-rays through a stationary object having varyingpermeabilityto X-rays to generate a first X-ray signal, applying to said screen said first X-ray signal and simultaneously applying across said screen an alternating electric field toefect a phosphor-screen `presensitization varying in degree according to the quantity of X-rays applied thereto, removing from said presensitized screen said applied X-ray signal, thereafter removing from across said screen said applied electlic ield, repassing selected intensity X-rays through said object to generate a second X-ray signal, and applying said second X-ray signal to said screen to produce thereon a transient luminous object image Varying in luminosity with the varying X-ray intensity of said second X-ray signal and with the degree of screen presensitization previously effected, whereby the contrast between individual portions of the transient object image formed on said screen is increased.

5. The process of varying the contrast in the luminous response to an X-ray signal of an X-ray-responsive phosphor screen characterized by displaying an enhanced luminous output when irradiated by X-rays and simultaneously placed within the inuence of an alternating electric field, said process comprising passing selected intensity X-rays through a stationary object having varying permeability to X-rays to generate a first X-ray signal, applying to said screen said tirst X-ray signal and simultaneously applying across said screen an alternating electric field to effect a phosphor-screen presensitization varying in degree according to the quantity of X-rays applied thereto, removing from said presensitized screen said applied X-ray signal and said applied electric iield, repassing selected intensity X-rays through said object to generate a second X-ray signal, and applying said second X-ray signal to said screen to produce thereon a transient luminous object image varying in luminosity with the varying X-ray intensity of said second X-ray signal and with the degree of screen presensitization previously eiected, and recording said transient luminous image, whereby the contrast between individual portions of the transient object image formed on said screen is varied.

6. The process of increasing the luminous response to an X-ray signal of an X-ray-responsive phosphor screen characterized by displaying an enhanced luminous output when irradiated by X-rays and simultaneously placed within the iniiuence of an alternating electric field, said process comprising passing selected intensity X-rays through a stationary object having varying permeability to X-rays to generate a first X-ray signal, applying to said screen said first X-ray signal and simultaneously applying across said screen an alternating electric field to eiect a phosphor-screen presensitization varying in degree according to the quantity of X-rays applied thereto, removing from said presensitized screen said applied X-ray signal and said applied electric field, repassing relatively intense X-rays through said object to generate a second X-ray signal, and applying said second X-ray signal to said screen to produce thereon a transient luminous object image varying in luminosity with the varying X-ray intensity of said second X-ray signal and with the degree of screen presensitization previously eifected, whereby the luminous intensity of the transient object image formed on said screen is increased.

7. The process of varying the contrast and enhancing the luminous response to an X-ray signal of an X-ray responsive phosphor screen characterized by displaying an enhanced luminous output when irradiated by X-rays and simultaneously placed within the influence of an alternating electric field, said process comprising passing selected intensity X-rays through a stationary object having varying permeability to X-rays to generate a tirst X-ray signal, applying to said screen said first X-ray signal and simultaneously applying across said screen an alternating electric lield to effect a phosphor-screen presensitization varying in degree according to the quantity of X-rays applied thereto, removing from said presensitized screen said applied X-ray signal and said applied electric field,

repassing relatively intense X-rays through said object to generate a second X-ray signal, and applying said second -ray signal to said screen to produce thereon a transient luminous object image varying in luminosity with the varying X-ray intensity of said second X-ray signal and with the degree of screen presensitization previously effected, whereby the contrast between individual portions of the transient object image formed on said screen is varied and the luminous intensity of the transient object image is enhanced. n

8. The process of increasing the contrast and enhancing the luminous response to an X-ray signal of an X-ray responsive phosphor screen characterized by displaying an enhanced luminous output when irradiated by X-rays and simultaneously placed within the iniiuence of an alternating electric field, said process comprising passing selected intensity X-rays through a stationary object having varying permeability to X-rays to generate a first X-ray signal, applying to said screen said first X-ray signal and simultaneously applying across said screen an alternating electric eld to effect a phosphor-screen presensitization varying in degree according to the quantity of X-rays applied thereto, removing from said presensitized screen said applied X-ray signal and said applied electric field, repassing relatively intense X-rays through said object to generate a second X-ray signal, applying said second X-ray signal to said screen to produce thereon a transient luminous object image varying in luminosity with the varying X-ray intensity of said second X-ray signal and with the degree of screen presensitization previously effected, and stopping said relatively intense X-ray irradiation immediately after said transient image has been produced on said screen, whereby the luminous intensity of the transient object image formed on said screen is increased and the luminous intensity of the transient object image is enhanced without appreciably increasing the quantity of X-rays to which said object is exposed.

9. The process of increasing the contrast and enhancing the luminous response to an X-ray signal of an X-ray responsive phosphor screen characterized by displaying an enhanced luminous output when irradiated by X-rays and simultaneously placed within the influence of an alternating electric field, said process comprising passing selected intensity X-rays through a stationary object having varying permeability to X-rays to generate a first X-ray signal, applying to said screen said first X-ray signal and simultaneously applying across said screen an alternating electric field to effect a phosphor-screen presensitization varying in degree according to the quantity of X-rays applied thereto, removing from said presensitized screen said applied X-ray signal and said applied electric field and repassing relatively intense X-rays through said object to generate a second X-ray signal, applying said second X-ray signal to said screen to produce thereon a transient luminous object image varying in luminosity with the varying X-ray intensity of said second X-ray signal and with the degree of screen presensitization previously elected, recording said transient object image, and stopping said relatively intense X-ray irradiation immediately after said transient image has been produced on said screen and recorded, whereby the contrast between individual portions of the transient object image formed on said screen in increased and the luminous intensity of the transient object image is enhanced without appreciably increasing the quantity of X-rays to which said object is exposed.

References Cited in the le of this patent 

